Potent airway smooth muscle relaxant effect of cynatratoside B, a steroidal glycoside isolated from Cynanchum stauntonii.

The dried roots of Cynanchum stauntonii in having cough-relieving efficacy are commonly included in traditional antitussive formulas. The active components in a C. stauntonii root extract responsible for airway relaxation were isolated using an ex vivo bioassay-guided fractionation method, in which subfractions were evaluated for their inhibitory effects on the contraction of isolated rat tracheal rings by isometric tension measurements. A steroidal glycoside, cynatratoside B (1), identified by LC-MS and NMR spectroscopic analysis, was shown to have potent inhibition on acetylcholine- and carbachol-induced tracheal contractions. The present data provide scientific evidence to support the traditional use of C. stauntonii as an antitussive herbal medicine.